Lymphatics I

intracellular fluid (ICF)

abt 2/3 of the total body fluids

extracellular fluid (ECF)

a third of total body fludis

blood (plasma) and interstitial (tissue) fluid

provides the nutrients cells need

interacts with ICF across the plasma membrane

body fluid distribution

hydrostatic and osmotic forces control the movement of fluid between the tissue spaces and the capillaries, affecting blood volume

urine formation and water intake (drinking) also affect blood volume

total volume of intracellular and extracellular fluid is normally maintained constant by a balance between water loss and water gain

hydrostatic pressure (HP)

pressure exerted by blood within capillaries or by tissue fluids

capillary hydrostatic pressure is ~34mmHg (arterial end) and ~14mmHg (venous end)—causes fluid to filter out of the capillaries into the tissues

tissue hydrostatic pressure varies, low, ~1mmHg~opposes filtration out of capillaries

net hydrostatic pressure

= capillary HP - tissue HP

favors the movement of fluid out of the capillaries

capillary filtration

glucose, comparably sized organic molecules, inorganic salts, and ions are filtered along with water through the capillary pores into the tissue fluid

larger molecules like plasma proteins retained in the capillaries

plasma protein concentration (6 to 8 g/100 mL) is therefore higher than interstitial fluid protein concentration (2 g/100 mL)

colloid osmotic pressure

pressure exerted by proteins dissolved in a fluid

draws fluid in

plasma colloid osmotic pressure (20mmHg) greater than tissue fluid colloid osmotic pressure (~0mmHg) due to greater concentration of proteins in the plasma as compared to tissue fluid

oncotic pressure

the difference between plasma colloid osmotic pressure and tissue fluid colloid osmotic pressure

oncotic pressure = 20mmHg

favors the movement of fluid into the capillaries

starling forces

opposing forces of hydrostatic pressure and oncotic pressure that predicts movement of fluid across capillary membranes

fluid movement factors

(HPc - HPt) - (OPc - OPt)n

net hydrostatic pressure

(HPc - HPt)

(OPc - OPt)

net oncotic pressure

HPc

hydrostatic pressure in capillary

HPt

Hydrostatic pressure of tissue fluid

OPc

Colloid osmotic pressure of blood plasma

OPt

Colloid osmotic pressure of tissue fluid

distribution of fluid across capillary walls

favor movement of fluid out of the capillaries at the arteriole end (positive value) and into the capillaries at the venule end (negative value)

only 85-90% of fluid filtrate returs to capillaries at venule end

10-15% remains in the tissue spaces and re-enters venous system via lymphatic vessels

oedema

excessive accumulations of tissue fluids

oedema causes

high arterial blood pressure

venous obstruction

leakage of plasma proteins into interstitial space

decreased plasma protein concentration

obstruction of lymphatic drainage

the lymphatic system

network of organs and vein-like vessels that recover fluid lost from the circulatory system

the lymphatic system functions

return fluid to the bloodstream

immune defense

fat transport

return fluid to the bloodstream

returns ~3L of protein containing fluid from the interstitial fluid to the blood

immune defense

inspect it for disease agents and active immune responses

macrophages filter lymph, and b & t lymphocytes provide immunity

fat transport

transport fat and fat soluble vitamins (A, D, E, K) from GI to blood

the lymphatic system fluid recovery

fluid continually filters from the blood capillaries into the tissue spaces

blood capillaries reabsorb 85%

15% (2-4L/day) of the water and about half of the plasma proteins enter the lymphatic system and then are returned to the blood

helps restore the fluid balance

primary lymphatic organs

where lymphocytes are formed and mature

provides an environment for stem cells to dicide and mature into B- and T-cells

primary lymphatic organ examples

bone marrow

thymus

secondary lymphatic organs

the tissues are arranged as a series of filters monitoring the contents of the extracellular fluids

i.e. lymph, tissue fluid, and blood

where lymphocytes are activated

secondary lymphatic organ examples

spleen

lymphnodes

tonsils

peyer’s patches

mucosa associated lymphoid tissue

largest lymphoid organ

spleen

MALT

mucosa associated lymphoid tissue

lymph

refers to the fluid that enters the lymph cappilaries from the interstitial fluid

similar in composition to blood plasma with less protein and more fat

looks clear or faintly opalescent

the excess water and solutes that filter out of the capillary are picked up by the lymph vessels and returned to the circulation

lymphatics (lymphatic vessels)

structure is similar to veins but thinner, with numerous valves and associated with lymph nodes

extensively located, and normally arrange in 2 sets—one deep and one superficial

they normally carry lymph through lymph nodes and to larger lymphatic ducts

afferent vessels go into into a lymph node, and efferent vessels go OUT of lymph nodes

NO lymph vessels in the CNS, bone marrow, bone, and cornea

lymphatic trunks

structured like veins

collect lymph from lymphatic and deliver it to the large lymphatic ducts, which are structured like large veins carrying lymph into the subclavian veins

right lymphatic duct

1.25cm long

junction of the right jugular vein and the right subclavian vein

drains the upper right limb, the right side of the head, neck, and thorax

thoracic duct

38-45cm long

extends from L2 to the left subclavian vein

lies in the midline of the thorax, near the aorta

begins as a dilation called the cisterna chylii

drains lymph from the rest of the body

lymphoid cells

lymphocytes

macrophages

dendritic cells

reticular cells

lymphocytes

arise in red bone marrow then migrate to other tissues to become immunocompetent

B lymphocytes

T lymphocytes

B lymphocytes

produce antibody secreting plasma cells

T lymphocytes

fight antigens directly and regulate the immune response

macrophages

phagocytose antigens and help to activate T cells

dendritic cells

antigen presenting cells found in mucosal membranes and in the skin

reticular cells

connective tissue cells that produce reticular fibers for the stroma that support other lymphoid cells in lymphoid tissue

lymphoid tissue

made of reticular fibers (stroma) and lymphoid cells (macrophages, lymphocytes)

diffuse lymphoid tissue

lymphoid follicles

places where lymphoid nodules can be found: lymph nodes, peyer’s patches, appendix

diffuse lymphoid tissue

small areas of un-encapsulated tissue found in most organs and in lamina propia of mucous membranes

lymphoid follicles

like diffuse tissue, but has a greater density of fibres

swollen glands

swollen cervical nodes

may have tenderness or pain

response to bacterial or viral infection, rarely due to cancer

sentinel node

the first few lymph nodes to which cancer spreads

in sentinel node biopsy, a tracer material is used to help the surgeon find the sentinel nodes during surgery

the sentinel nodes are removed and tested in a lab

if the sentinel nodes are free of cancer, then cancer probably hasn’t spread

lymphatic obstruction

lymphedema

myxedema

filariasis

lymphedema

swelling due to build-up of lymph fluid in the body

myxdema

hypothyroidism that leads to swelling and pretibial skin changes

filariasis

a parasitic disease caused by microscopic, thread-like worms